Such disconnectable rotor locks have the significant advantage from the security point of view that they cannot be forced by rotation, since forcible rotation acts on the sleeve, or intermediate stator (which remains secured with respect to the rotor by the locking means), in such a way that the above mentioned coupling means cannot be activated, so that the bolt actuating member for the lock bolt is also not operated. Similarly, such locks are difficult to open by axial penetration into the lock mechanism, such as an attempt to make a sectional cut in order to try to reach the locking means, since the piercing tool tends to cause the rotor, and the stator sleeve with it, to rotate in such a way that, again, the bolt actuating member will not operate.
A lock of the above mentioned kind is described for example in European Patent Publication EP 0 151 081A. The lock described in that publication includes coupling means, coupling the rotor to a bolt actuating member, which comprise a finger coupled for rotation with the rotor, the axis of rotation of this finger being normally coaxial with that of the rotor but being capable of being displaced off centre only when the rotor rotates by itself.
Such a lock does however have various disadvantages. In particular, its construction is complicated and cumbersome, which makes it difficult to use in practice when the lock is required to be economical and to occupy a small volume.
It has also been proposed to make the rotor, or part of the rotor, slideable with respect to the stator sleeve when, but only when, the correct key is inserted, in such a way that the rotor engages with the bolt actuating member after this sliding movement. Such a lock, apart from the considerable length which it must have to allow the rotor to slide, has the disadvantage that it is subject to substantial wear because of the sliding action of the rotor, with all or part of the locking means, every time the bolt is opened or closed. In addition, it requires very high precision in the locking members (constituting the locking means) themselves, and a very small clearance between the rotor and the stator sleeve in order to satisfy the requirements of security.